Who developed the Gram stain technique?

A. To differentiate between Gram-positive and Gram-negative bacteria: Differentiating Gram-positive from Gram-negative bacteria is the purpose of Gram staining, a differential staining technique. Simple staining does not distinguish between bacterial cell wall characteristics or species based on Gram reaction.

B. To determine bacterial motility: Bacterial motility is assessed using methods such as the hanging drop technique or motility agar. Simple staining does not provide information about motility because it stains all cells uniformly and immobilizes them on the slide.

C. To visualize the size, shape, and arrangement of bacteria: The primary purpose of simple staining is to enhance the contrast between bacterial cells and the background, allowing clear observation of cellular morphology, including size, shape (cocci, bacilli, spirilla), and arrangement (chains, clusters, pairs). This information is fundamental for bacterial identification and classification in microbiology.

D. To identify bacterial endospores: Endospore identification requires special staining techniques, such as the Schaeffer-Fulton method using malachite green and safranin. Simple staining cannot differentiate spores from vegetative cells because all structures take up the basic dye similarly.

A. Lactose: Lactose in Eosin Methylene Blue (EMB) agar serves as a fermentable carbohydrate source. It allows differentiation of bacteria based on their ability to ferment lactose, producing color changes in the colonies, but it does not inhibit Gram-positive bacteria.

B. Agar: Agar is a solidifying agent that provides a stable surface for microbial growth. It is inert and does not selectively inhibit any bacterial group; its role is purely structural.

C. Eosin and methylene blue dyes: The eosin and methylene blue dyes in EMB agar act as selective agents that inhibit the growth of Gram-positive bacteria while allowing Gram-negative bacteria to grow. These dyes also serve as pH indicators, producing color changes in colonies that ferment lactose, which aids in differentiation of coliforms and other Gram-negative bacteria.

D. Sodium chloride: Sodium chloride maintains osmotic balance in the medium but does not selectively inhibit Gram-positive bacteria. Its concentration is not sufficient to act as a selective agent in EMB agar.